Semiconductor device fabrication involves performing a variety of processes, procedures and operations in order to achieve a fabricated device. These operations include, but are not limited to, layering, doping, heat treatments, and patterning. Layering is the operation used to add layers of a selected thickness to a wafer surface. These layers can be insulators, semiconductors, conductors, and the like and can be grown or deposited by a number of suitable methods (e.g., chemical vapor deposition, sputtering, and the like).
Doping is the process that introduces specific amounts of dopants in the wafer surface through openings in surface layers. Two general techniques of doping are thermal diffusion and ion implantation. Doping is used, for example, to create active regions in transistors.
Heat treatments are operations in which a wafer is heated and cooled to achieve specific results. Generally, no additional material is added although contaminates and vapors may evaporate from the wafer surface. A common heat treatment is called an anneal which is employed to repair damage to crystal structures introduced by ion implantation.
Patterning is the operation that employs a series of steps that results in the removal of selected portions of added surface layers. After removal, a pattern of the layer is left on the wafer surface. The material removed can be in the form of a hole in the layer or a remaining island of the material. The patterning operation is also known by the names of photomasking, masking, photolithography, and microlithography.
Another important operation is chemical mechanical planarization (CMP), which can be employed in patterning operations. Generally, planarization is a process by which a wafer topography is made substantially flat or planar. CMP is a type of planarization process in which chemical and mechanical components are employed to planarize a wafer surface. Typically, a slurry comprised of a chemical component and mechanical components (e.g., abrasive particles) is flowed onto a wafer surface and a rotating pad is pressed against the wafer surface. The components chemically and mechanically remove portions of the wafer surface. The combined actions of the slurry and the rotating pad result in a polishing operation that can planarize the wafer surface.
In order to achieve a planar surface, it is important that the polishing pad be substantially spatially uniform with regard to compressibility. Non-uniformities can result in defects and/or a non-planar surface. Accordingly, it is desirable that a polishing pad be able to maintain its uniformity with regard to compressibility even after repeated use.